The National Ambulatory Medical Care Survey (NAMCS), conducted by the National Center for Health Statistics, is an annual national probability sample survey of visits to the offices of physicians classified by the American Medical Association (AMA) and American Osteopathic Association (AOA) as [unreadable]office-based, patient care.[unreadable] Federally employed physicians, specialists in anesthesiology, radiology, or pathology;and physicians who do not see patients in an office are excluded. NAMCS utilizes a multistage probability design that involves probability samples of primary sampling units (PSUs), physician practices within PSUs, and patient visits within practices. The sample includes about 4,000 physicians and 30,000 visits annually. Data are obtained on patients'symptoms, physicians'diagnoses, and services ordered or provided.